Climbs in Garmin connect vs on 530

Hi,

I always have a big difference in the amount of climbs detected by my Edge compared to my mates’ Wahoo. In the last ride we did together, he had 35 and I had 16. Now of course, different brands and settings and algorithms, but what was really odd is that my garmin connect - when I uploaded the gpx to create the course on my edge - says 24 climbs. But then when uploaded, it only has 16 on edge even if it has been set to “all climbs. 
any ideas?